DOING THE LIMBO WITH A LOW BARRIER: Hydrogen Bonding and Proton Transfer in 6-Hydroxy-2-Formylfulvene ZPE Zero Point Energy ZPE Zachary N. Vealey, Deacon J. Nemchick, Lidor Foguel, & Patrick H. Vaccaro Department of Chemistry, Yale University 225 Prospect St., New Haven, CT 06520 USA

Reaction Coordinate Potentials Weak Bond Intermediate Bonds Strong Bond A Spectroscopic Metric for Proton-Transfer Rate A············H—D A·············H—D D—H············A A·········H········A D—H············A D—H·············A Symmetric Well with High Barrier Symmetric Well with Low Barrier Symmetric Well with No Barrier Asymmetric Well HFF 6-Hydroxy-2-FormylFulvene

6-Hydroxy-2-Formylfulvene (HFF) No Barrier Low Barrier vs. Symmetric EQ Structure Asymmetric EQ Structure Bulk-gas MW Δ ≈ 150 ± 20 cm-1 Rapid 100 fs proton-transfer rate Liquid NMR/IR studiesb Bulk-gas XPSc Supports discrete proton-transfer dynamics a b C. L. Perrin and B. K. Ohta., Bioorg. Chem. 30(1), 3-15 (2002). a H. M. Pickett, J. Am. Chem. Soc. 95(6), 1770-1774 (1973). c R. S. Brown, et. al, J. Am. Chem. Soc. 101 (12), 3157-3162 (1979).

Experimental Setup Trot << 5 K Spectral Resolution ~ 0.06 cm–1

U.S. National Science Foundation Summary & Conclusions HFF affords a model system for exploring the synergism between proton transfer and low-barrier hydrogen bonding. Vibronically-resolved information has been obtained for the ground and (π*π) excited states of HFF and HFF-d. LIF spectra show extensive excited-state progressions built upon modes that modulate the reaction site. DF spectra reveal evidence of ground-state tunneling dynamics characterized by and Multiple-resonance spectroscopy (FHB, SEP, RFWM) will be deployed to elucidate vibrational landscapes and tunneling dynamics. Weakly bound complexes formed with hydrogen-bonding and inductively-coupled ligands will be interrogated to explore incipient solvation effects. Supported by: U.S. National Science Foundation